Polyolefins may be used to produce injection molded articles and containers for food products. Polypropylene heterophasic compositions, due to their impact resistance properties that extend at low temperatures, can be used in the production of containers for frozen food products. While polymers for the injection molding may have a a high melt flow rate (MFR), the high MFR can be detrimental for some mechanical and optical properties.
WO 2006/114357 relates to a propylene polymer composition comprising (weight percentages being
referred to the sum of A+B):
(A) 60-90% by weight of a copolymer of propylene with ethylene containing less than 2.5% wt of ethylene units; and
(B) 10-40% by weight of a copolymer of propylene comprising from 15 to 35% wt of ethylene units,
said polymer composition having a melt flow rate value according to ISO 1133 (230° C., 2.16 Kg) of less than 10 g/10 min
Even if these compositions show good values of Haze and Izod the MFR may be too low to be used in injection molding.
US 2004/0266952 relates to a propylene polymer composition comprising (percent by weight):
A) from 50 to 90% of one or more propylene copolymer(s) having a content of moiety insoluble in xylene at room temperature of not less than 85%, selected from the group consisting of (A1) random copolymers of propylene with ethylene containing from 1 to of ethylene; (A2) copolymers of propylene with one or more C4-C8 a-olefin(s) containing 2-10% of the C4-C8 a-olefin(s); and (A3) copolymers of propylene with ethylene and one or more C4-C8 a-olefin(s) containing 0.5-5% of ethylene and 2-6% of C4-C8 a-olefins; and
B) from 10 to 50% of a copolymer of propylene containing from 8 to 40% of ethylene and optionally 1-10% of a C4-C8 a-olefins;
wherein the propylene polymer composition has an MFR (2) value of from 3 to 30 g/10 min obtained by subjecting to degradation a precursor composition comprising the same copolymers (a) and (b) in the above said proportions having an MFR (1) value of from 0.1 to 5 g/10 min, with a ratio MFR (2) to MFR (1) of from 1.5 to 20.
In the examples the value of impact properties of the visbroken polymer may be high, however, the haze measured on a film may be low.
The applicant found a propylene polymer composition containing propylene and ethylene having an high MFR can be fine-tuned in order to achieve an optimum balance of mechanical and optical properties for the production of injection molded articles, such as containers.